The present invention relates to integrated circuit (IC) fabrication technology, and more particularly, to a method of fabricating IC having a sealed cavity.
Some products use packaging technology that involves bonding a cap over a predetermined area of a substrate to create a hermetically sealed cavity. The hermetically sealed cavity is often formed to protect sensitive circuit elements therein. FIG. 1 is a perspective illustration of a sample apparatus 10 including a device chip 20 having a substrate 22 and circuit elements 24 fabricated on the substrate 22. A cap 30 is attached over the device chip 20 creating a hermetically sealed cavity within which the circuit elements 24 are protected.
FIG. 2 illustrates a cut-away side view of the apparatus 10 of FIG. 1 after the bonding process. The hermetically sealed cavity is indicated by reference number 26. As illustrated, bottom of the hermetically sealed cavity 26 is defined by the device chip 20 including the substrate 22 and the circuit elements 24. The top of the hermetically sealed cavity 26 is defined by the cap 30. The sizes of the device chip 20 and the cap 30 can vary greatly depending on implementation but can be, for example, on the order of millimeters (mm) or fractions of millimeters, for example, about 0.5 mm to 2 mm.
Sides of the hermetically sealed cavity 26 are defined by gasket 32 which can be a part of the cap 30. The gasket 32 is attached to the substrate 22 using bonding metal 34 such as pure gold. To achieve the hermetically sealed cavity 26, the bonding agent 34 is applied to the substrate 22, the gasket 32, or both. For the bonding metal 34, pure gold (chemical symbol Au) is often used. Then, the device chip 20 and the cap 30 are pressed together and heated to promote diffusion bonding. The gasket 32 can be about 1 to 10 microns thick.
For some applications, pure gold is used as the metal bonding agent 34 for diffusion bonding of the cap 30 on to the device chip 20. For pure gold, bonding parameters (such as level of pressure, temperature, and diffusion time) to achieve a desirable level of diffusion bond quality are known. However, for other applications, these bonding parameters may be procedurally undesirable or even unachievable. Accordingly, there remains a need for a method of manufacturing an apparatus with sealed cavity that allows for more flexible bonding parameters.